1. Field of the Invention
The invention relates to a sensor element and a method for the detection of a parameter of a gas mixture in a gas chamber.
2. Detailed Description of Prior Art
To detect an air/fuel mixture composition of an exhaust gas in an exhaust system of an internal combustion engine, modern motor vehicles comprise one or more solid state electrolyte sensors in the exhaust system. Such solid state electrolyte sensors are also referred to as lambda probes. The solid state electrolyte sensors each comprise a solid body with electrolytic properties, i.e. the solid body has the ability to electrically conduct certain ions. Lambda probes are known in numerous different embodiments.
DE 38 34 987 A1 discloses a sensor element for limiting current sensors for the determination of the lambda value of gas mixtures, especially the exhaust gases of internal combustion engines, with outer and inner pump electrodes disposed on an O-2 ion-conducting solid electrolyte, of which the inner pump electrode is accessible to the measurement gas passed through a diffusion gap and the diffusion gap is covered by the solid electrolyte, and in which the solid electrolyte forming the cover for the diffusion gap is a solid electrolyte layer formed by printing onto a ceramic carrier using screen printing technology.
DE 20 2004 015 400 U1 discloses a sensor both for oxygen measurement and for volumetric flow measurement and/or incident flow measurement, having on a region of a first surface of a plate-shaped support made of an electrical insulator successive layers of a solid state electrolyte, electrodes with connecting tracks and a diffusion barrier, which covers one of the electrodes up to its connecting track. A layer of an electrical conductor is disposed on a region of a second surface opposite the first surface of the plate-shaped support as at least one heating element.
EP 0 152 942 A2 discloses a device for the detection of an air-fuel ratio of a fuel mixture. The device comprises a partition with a first side and a second side. On the first side the partition bounds a volume that receives atmospheric air and that is pneumatically coupled to ambient atmosphere, and on the second side a volume that receives exhaust gases and that is pneumatically coupled to a source of the exhaust gases. The partition encloses at least one section of an oxygen ion-conducting solid state electrolyte. Furthermore, the device comprises a first electrode exposed to the atmospheric air, and a second electrode exposed to the exhaust gas, wherein the oxygen ion-conducting solid state electrolyte is disposed between the first and second electrode. Furthermore, the a device comprises a limiter to limit the gas diffusion of the exhaust gases to the gas-receiving volume.
DE 31 08 305 A1 discloses a polarographic measurement sensor for the determination of the lambda equivalence point in exhaust gases, which operates according to the diffusion limit current principle, with an oxygen ion-conducting solid electrolyte body in the form of a small plate that carries an anode on one side and a cathode on the other side, to which a constant voltage can be applied. The cathode is covered by a diffusion barrier in the form of a porous layer and both electrodes are exposed to the gas to be measured. The cathode is divided into two partial cathodes, which are juxtaposed in the measurement region, and that one partial cathode is more cathodically polarized than the second partial cathode.
EP 0 607 385 A1 discloses a sensor for the determination of the concentration of specified components in the exhaust gas of internal combustion engines. The sensor comprises a pump cell whose cathode is provided with a first diffusion barrier and whose anode is provided with a second diffusion barrier. In an alternative embodiment the sensor comprises a reference electrode that is not loaded in the measurement gas for measuring the polarization of at least one of the electrodes relative to said reference electrode.
DE 196 10 911 A1 discloses a device for the determination of the partial pressure of a gas in a gas mixture, especially in air, with a gas sensor comprising a measurement chamber with a wall formed by a solid electrolyte and comprising at least one pair of electrodes, whose inner electrode is disposed in the measurement chamber and whose other outer electrode is in contact with the gas mixture. Furthermore, the device comprises a control unit, which is provided to apply a pump voltage to a pair of electrodes associated with the solid electrolyte during operation to generate a pump current. The control unit interrupts the pump current at times. Furthermore, the device comprises a measurement unit, which during the no-current period measures the potential difference between an electrode pair associated with the solid electrolyte, the potential difference being produced by a Nernst voltage.